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I know that, most of the time, heat transfer and conductance go hand in hand. But is there some material that is an electric insulator while being good (or at least not that bad) at heat transfer?

I don't need extreme solutions such as in this question:

Is there a material that conducts heat well and has a very high melting point, but is also an insulator?

Put simply, I have a laptop from which top cover(aluminium plate) could be removed for a long period of time (and even forever) while the motherboard is still operating. The motherboard should be protected from dust and operator curiosity. So I need to close the laptop with a thin layer of a material that should :

  • protect the user from shock hazards (from typical currents and intensities you find in laptop motherboard)
  • be thin.
  • help dissipate moderate heat (rest of the enclosure will be in aluminum and there will be a fan so temp should be well below 100°C)
  • be puncture resistant if someone put his finger and press it against underlying PCB.

Surface will be around 30 x 15 cm.

I welcome any other suggestion.

EDIT:

When I think about it, it looks like I exactly described a thermal pad. Would a thermal pad provide an effective protection against shocks? I guess if this is designed to not short circuit the board then a fortiori it will protect humans.

v1nce
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    A diamond is the best heat conductor, but an electrically it is insulator. Probably not very suitable for your application though... – Eugene Sh. Aug 08 '22 at 21:17
  • That the solution suggested in the linked EE. Too extreme and impractical for me. Thank you anyway. – v1nce Aug 08 '22 at 21:22
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    What is wrong with the existing laptop enclosures? What are you trying to solve? – Eugene Sh. Aug 08 '22 at 21:25
  • Anodized aluminum or ceramic coated copper? – PStechPaul Aug 08 '22 at 21:30
  • @PStechPaul: anodized aluminium? with painted side on the pcb ? – v1nce Aug 08 '22 at 21:33
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    I think you need to quantify your electrical and heat conductivity requirements to get a meaningful answer. You might get better answers on the physics or engineering stacks. – Theodore Aug 08 '22 at 21:40
  • @Eugene Sh. top side of the enclosure (aluminium plate) could be removed for a brief or long time. When removed, I need the mainboard to be still safe for operator. So I'm looking for a very thin layer to protect the operator from hazard. As there could be a aluminium plate above it will be a bonus if this layer could transfer the heat to the aluminium plate. – v1nce Aug 08 '22 at 21:40
  • @Theodore you're probably right. I'm probably not skilled enough in EE to word it right. – v1nce Aug 08 '22 at 21:42
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    If we are talking about your typical laptop, the operating voltages are very low to be a hazard for the operator, assuming it is not connected to mains, or the power supply is not critically damaged to pass the mains voltage to the laptop. The only danger is to the equipment itself. – Eugene Sh. Aug 08 '22 at 21:43
  • @Eugene Sh. thank you for your comment. This is what I suspected – v1nce Aug 08 '22 at 21:46
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    Do you really "need the mainboard to be still safe for operator", or do you need it to be safe from the operator? There are no voltages high enough to be a shock hazard in any even remotely normal laptop, but exposing the innards would make it far more likely that someone careless would drop something in and break it. – brhans Aug 10 '22 at 00:35
  • The best material other than diamond for this would be beryllium oxide ceramic... Of course, that's horrifically toxic if broken or scratched or otherwise any dust from it gets into the air, so that's probably not a good solution either, if this is the sort of thing you'd use around humans or animals. – Hearth Aug 10 '22 at 15:41
  • Aluminum nitride is perhaps the best choice that isn't toxic or incredibly expensive; it's still a ceramic, though, so it's going to be brittle. Pressure won't puncture it, but it very well could fracture it. – Hearth Aug 10 '22 at 15:46
  • Do you need the electrical insulation in all directions, or is it acceptable if it's electrically conducting in two dimensions but insulating in the other, for instance? Do you need the heat conduction in all directions, or just within a plane or in a single dimension? – Hearth Aug 10 '22 at 15:47
  • @brhans my primary concern was about operator safety. Now that it seems it will be safe anyway, "protecting" the mainboard from dust or operator curiosity is another important goal. As the 'protective layer' I look for should be thin, it will probably fell onto the mainboard or be really close to it that's why it should be an insulator. – v1nce Aug 12 '22 at 16:49
  • @Hearth by puncture I thought not of a deliberate act with a needle or something like this, but more of damages that could result in operator pressing the layer to the mainboard with his fingers occasionnaly. I probably overstated this too because of the 'ductility' of fingers and the lack of really sharp element on the board – v1nce Aug 12 '22 at 16:56
  • @Heart thank you for your comments and time. You'll probably suggest some kind of new metamaterial which will be costly. I -more or less- abandon the heat transfer constraint. Some suggested very efficient heat transfer material (PGS) but point out the gaps between MB / Layer / (air or aluminium) should be carefully designed. As the thinness is really important I guess the layer will probably lacks of rigidity, so when used with a aluminium plate above the gaps would probably be inconsistent along the plane and will probably defeat the heat transfer property. – v1nce Aug 12 '22 at 17:18
  • If heat transfer isn't a concern, then I'd say just use a plastic sheet. Or even cardboard--you see that occasionally in 80s home computers and stuff, just a sheet of cardstock cut to the appropriate shape. – Hearth Aug 12 '22 at 17:41

1 Answers1

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You could go with ceramic heat spreaders or maybe pyrolytic graphite sheets if the electrical conductivity of 10000 S/cm is acceptable. If the power supply is <60VDC and its output is internally isolated from mains, the system can be made SELV but depending on the setup, you might want something a little more robust and I would not recommend using any of the materials as a structural component. There are also some more engineered heat spreader sheets that could fit the bill and many other types of thermal pads/sheets that can effectively transfer heat from your motherboard to the case while also preventing e.g. case flexure from shorting out the circuit.

Edited to incorporate some of your comments.

vir
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  • As thinness matters, pyrolytic graphite sheets look like a very good choice. – v1nce Aug 08 '22 at 21:52
  • There should be no (or little) flexure of the pcb or enclosure. – v1nce Aug 08 '22 at 21:57
  • The gap between the board and the case is an important variable when choosing a thermal interface pad, as is the difference in height between components. Some pads are optimized for narrow gaps between two plane surfaces and require very high mounting pressures for optimal performance; these are almost like sheets of thermal grease. Some are more sponge-like and are designed to accommodate variance in gap width (gap filler pads). If you have components putting out lots of heat - high performance processors, regulators, etc - the time to perform a detailed thermal analysis is now. – vir Aug 08 '22 at 22:05
  • When I see thermal conductivity of PGS are well above aluminium, i think I overstated my needs in thermal conductivity. I need the sheet to "not block that much" heat transfer so that it could transfer it to the aluminium plate that could be above the thin layer. But this would be more of a bonus to help cooling that already takes place in the rest of enclosure. So if price is not a problem (will check) PGS look really nice. Otherwise I'll go for other heat-conductive sheets. – v1nce Aug 08 '22 at 22:08
  • PGS is more for spreading heat within the plane of the sheet rather than from one face to another. From what I gather of your application, I do not think that PGS is the optimal material. – vir Aug 08 '22 at 22:09
  • The more I think about it, the more my problem looks like a simple electric insulation issue. I don't want the user to be able to short-circuit the board or suffers from hazard. As there could be an aluminium plate 'above' I thought it will be nice to use it to dissipate heat. But there will be too many issues (those you cite) for a marginal gain. – v1nce Aug 08 '22 at 22:15